This application is based on and incorporates herein by reference Japanese Patent Application No. 2000-98014 filed on Mar. 31, 2000.
1. Field of the Invention
The present invention relates to a brake device actuator and a brake device having the same.
2. Description of Related Art
It has been proposed to provide a vehicular brake device that is actuated by an actuator having an electric motor as its driving source. Furthermore, several such vehicular brake devices employ an electric parking brake actuation mechanism instead of a well known cable operated parking brake actuation mechanism. This is due to a fact that the cable operated parking brake actuation mechanism generally has more components than the electric parking brake actuation mechanism. Thus, the cable operated parking brake actuation mechanism generally requires a tedious and time consuming assembling operation.
One brake device having the electric parking brake actuation mechanism is disclosed in U.S. Pat. No. 5,219,049 (corresponding to Japanese Examined Patent Publication No. 6-100239). In this brake device, when the parking brake is activated, an output shaft (rotor), of an actuator is rotated to actuate brake shoes. Once the brake shoes are actuated, the output shaft of the actuator is locked, so that free rotation of the output shaft of the actuator is prevented, thereby preventing movement of the brake shoes to holds the brake shoes in place.
However, the above parking brake actuation mechanism still disadvantageously includes a relatively large number of components.
To solve the above described disadvantages, one type of actuator has been proposed (U.S. patent application Ser. No. 09/592,415 corresponding to Japanese Patent Application No. 11-321479). This actuator has fewer components than the above described prior art. Furthermore, this actuator includes a slipping prevention unit (xe2x80x9clock mechanismxe2x80x9d) that prevents forceful rotation of an output shaft of a driving motor by an external force transmitted, for example, from the brake shoe side. This unit includes a regulation gear that is provided to regulate the rotation of the output shaft of the driving motor. When the regulation gear is engaged with a pinion secured to the output shaft of the driving motor, the rotation of the output shaft is restricted. On the other hand, when the regulation gear is disengaged from the pinion, the rotation of the output shaft of the driving motor is allowed. Forceful rotation of the regulation gear by vibrations and/or shocks during running of the vehicle is prevented by engaging an engagement recess of the regulation gear with an engagement pin to prevent improper engagement between the pinion and the regulation gear.
However, in this actuator, it is required to provide a limiting member, such as the engagement pin, an elastic unit for biasing the engagement pin or the like, for preventing rotation of the regulation gear during running of the vehicle. Furthermore, in order to release the regulation gear from the engagement pin, a switching motor (acting as an electric switching means) that drives the regulation gear must have an enough torque to overcome the engagement between the engagement recess of the regulation gear and the engagement pin. As a result, the switching motor is disadvantageously required to have a larger output torque to overcome this engagement.
The present invention addresses the above-described disadvantages. Thus, it is an objective of the present invention to provide a brake device actuator that has a reduced number of components and capable of preventing the improper engagement between the pinion and the regulation gear in the lock mechanism without increasing the output torque of the electric switching means. It is another objective of the present invention to provide a brake device including such a brake device actuator.
To achieve the objectives of the present invention, there is provided an actuator for actuating a brake device. The brake device includes a rotatable body and a friction member. The rotatable body is connected to an axle shaft of a vehicle and integrally rotating with the axle shaft. The friction member is movable between an engaged position where the friction member is biased into engagement with the rotatable body to apply a braking force against the rotatable body and a disengaged position where the friction member is disengaged from the rotatable body. The actuator includes an electric driving means, a driving force transmitting means, a regulating means and an electric switching means. The electric driving means generates a driving force to move the friction member between the engaged position and the disengaged position. The driving force transmitting means transmits the driving force of the electric driving means to the friction member. The regulating means is movable between a transmission prohibiting position where transmission of the driving force by the driving force transmitting means is prohibited and a transmission permitting position where the transmission of the driving force by the driving force transmitting means is permitted. The electric switching means switches the regulating means between the transmission prohibiting position and the transmission permitting position. The electric switching means is energized such that the electric switching means places and holds the regulating means in the transmission permitting position while the vehicle is running. Furthermore, there is also provided a brake device including the above-described actuator.